Research into the determinants of HIV risk behaviors among injection drug users, including individual, social, environmental and pharmacological factors, has taught us much in the past decade. Few investigations, however, have addressed all of these factors and their inter-relationships. Questions remain about the complex nature of antecedents to risky behavior, such as needle sharing and unprotected sex, in this population. Why are some individuals more likely to engage in risk behaviors than others? Are individual behaviors, such as self efficacy and negotiation skills, more important than social roles and relationships? Do pharmacological factors, such as the physically debilitating nature of heroin addiction have more influence on risk than environmental factors, such as paraphernalia laws? Do drug users differ in their general 'riskiness' compared to non-drug users? We are proposing to conduct a two-phase approach to understanding these issues. The first is a semi-structured qualitative assessment of current IDUs, crack smokers, and individuals who have never used drugs, focusing on antecedents to risk and the context and the circumstances in which risk taking occurs. The second, building on observations from the qualitative study, is a quantitative evaluation of predictors of risk taking, including individual, social, environmental and pharmacological factors. Particular emphasis will be placed on the role that gender plays in accounting for differences in risk. A comparison between current drug users and controls who have never used drugs, looking at differences in personality and psychological and social functioning will also be conducted. Findings from this investigation are intended to lead to the development of interventions that can reduce the occurrence of HIV risk behaviors among injection drug users.